It has been known in the prior art of exposed shackle padlocks to provide shackle assemblies for which a reciprocating movement between the shackle and the lock housing is required to open the padlock. The most common form of these padlocks comprises a relatively complex arrangement of locking members to latch and release the shackle relative to the padlock body. These padlocks have an inverted J-shaped shackle that when released, moves upwardly out of the body to achieve relative reciprocal movement. The short end of the shackle will then pivot to open only after clearing the padlock body, and the long end is entrained in the locking mechanism. These type of padlocks are generally called reciprocating shackle padlocks.
Another variation on this theme of relative reciprocal movement between the shackle and the padlock body is a reversal of parts as shown in Atkinson, U.S. Pat No. 3,837,189 issued Sept. 24, 1974. The Atkinson design padlock comprises an inverted U-shaped shackle with one end fractionally shorter than the other, and a lock body having an outer shell and an inner core which are adapted to move a constrained amount relative to each other. When the locking mechanism is activated to an "open" position, the shorter end of the shackle is released by downward movement of the outer shell. This permits the shackle to pivot open.
One serious problem with reciprocating padlocks is that internal space limitations do not provide sufficiently deep recess for the free end of the shackle. Due to the inherent play in the lock mechanism in securing the entrained end of the shackle, the shackle often can be pulled out a sufficient distance to clear the upper end of the padlock body to be pivoted open. There is nothing to prevent the shackle from pivoting once it clears the upper surface of the padlock body. The force necessary to open some padlocks is as little as 140 lbs; many high school-age young men can pull open such locks easily by hand.
Another disadvantage of many current padlocks is the use of rotary dials. Rotary dials can not be used in the dark or by many handicapped people, and often dexterous, fully sighted persons have difficulty opening such locks even in daylight. In addition, rotary dial operation is slow and requires relative precision of alignment of the dial markings with the index, and the settings are imprecise in all but the most expensive locks.
There are also disadvantages with the use of key locks. Keys are an inconvenience to carry around and can be easily lost or stolen. Most people would prefer to keep a combination in their head rather than to add another key to their key ring.
Push-button locks, such as the Cheng patent, U.S. Pat. No. 4,751,830, issued June 21, 1988, have significant advantages over rotary dial and key locks. The positive action of a push-button lock allows for quick, easy and accurate operation. They offer the relative pick-resistance of rotary dial locks in that they are combination locks, and also can be opened in the dark, or by sightless or physically handicapped persons. One disadvantage with current push-button padlocks is the amount of internal parts required which results in a padlock that is that is complex to assemble. Another disadvantage is that the padlocks are susceptible to being opened by a small prying forces as a result of the inherent amount of play in a exposed shackle reciprocating padlock.
Accordingly, there is a need in the art for a strong padlock that is easy to operate, inexpensive to assemble and has a simplicity that does not yield excessive play permitting opening by a small prying force.